In many types of conventional military aircraft a plurality of bombs may be carried within bomb bays by releasable shackle assemblies or the like, one shackle assembly being provided for each bomb. The shackle assemblies are suitably carried by bomb racks incorporated into the aircraft structure. For example, in a modern B-52 bomber, up to 84 five-hundred pound bombs may be carried in bomb racks within the bomb-bay and an additional 12 seven hundred and fifty pound bombs may be carried under each wing.
The shackle assemblies serve the dual purposes of releasably supporting the respective bombs in proper dropping orientation and also releasably supporting an arming link, lanyard or wire. The arming wire is attached to one or more arming mechanism latches or locks on the bomb and the arming mechanisms on the bomb are inoperative until the lock or latch is released.
The arming wire typically will be releasably retained with respect to a trigger unit which is carried by the shackle assembly. One portion of the arming wire will communicate with a latch or lock device such as a pin which locks a final arming device such as an arming propeller located adjacent the forward end of the bomb. This final arming propeller, which is actuated by airflow, must rotate a predetermined number of revolutions after drop before the bomb will explode. The pin prevents rotation of the final arming propeller until withdrawn from communication therewith by arming wire tension.
A bomb may additionally have a secondary arming mechanism adjacent the bomb fins. For example, barometric devices for air explosions often are provided to render the bomb finally armed when it reaches a predetermined altitude or alternatively, timing devices for delayed explosions may be provided to finally arm the bomb after a preset time has elapsed after drop. Should such a secondary arming mechanism be included other corresponding latch or lock devices are also provided and another portion of the arming wire cooperates therewith to prevent actuation of such secondary arming device until the lock device is released by arming wire tension.
The trigger unit is the means which renders the final and/or secondary arming devices operative. This typically has been accomplished by means of a selectively slidable pin which extends through a closed loop formed in the arming wire. When the bomb is released and drops clear of the shackle assembly the arming wire loop is retained by the pin of the trigger unit and the locking devices secured to opposite ends of the wire are thus withdrawn from the final and secondary arming devices to render them operative.
Should it be desired to abort a mission and drop inoperative or "dud" bombs, for example when mechanical or electrical difficulties with the aircraft require a forced landing or lightening of the cargo load, the trigger unit pin is withdrawn from the loop and the arming wire drops with the bomb. Thus, the arming assemblies are inactivated or inoperative and the bomb will not explode after drop.
Prior arming wire trigger units often work independently of the bomb release shackle assembly and are energized only when it is determined that an inoperative or "dud" bomb is to be released. This arrangement suffers from potential hazards of mechanical or electrical malfunction or human error with the resultant possibility that a live or armed bomb will be dropped when it is desired that a dud bomb be released. In other words, should the trigger pin of such prior trigger units inadvertantly not be withdrawn, a live, fully armed bomb will be dropped with potential catastrophic consequences.
One trigger unit which overcomes numerous prior art shortcomings is disclosed in U.S. Pat. No. 4,266,462 as a dual action trigger unit which must respond to the energization of the bomb release mechanism as well as to an independent safety mechanism before a live, fully armed bomb may be released. This arrangement greatly reduces the possibility of dropping live fully armed bombs when a dud release is in fact intended.
Typically, the prior art trigger units include lever type actuators wherein pivoted bar linkage systems are employed to transmit actuating motion to the trigger unit release pin. For example, in the above cited U.S. Pat. No. 4,266,462 a selectively positionable element offers the presence or absence of a fulcrum about which a link is pivotable. In the absence of the fulcrum the link merely pivots about its pivotal connection to the trigger pin upon movement of an actuator link whereas, when the fulcrum is provided, the pivotal link is pivotable about the fulcrum by the actuator link to retract the trigger unit pin and thereby release the arming wire.